What happens if you use a class that is not defined in the manifests directory?

When you attempt to use a class that has not been defined in the manifests directory, an error occurs. Puppet relies on the definitions outlined in your manifests to compile and apply configurations effectively. If you reference a class that does not exist in the appropriately specified directories, Puppet's compilation process will not find the class definition, leading to a runtime error indicating that the class could not be located. This behavior ensures that any configuration issues are caught early, promoting clarity and facilitating the debugging process.

In this context, simply ignoring the class or allowing it to work would lead to incomplete configurations, potentially resulting in a system that does not behave as expected. Puppet is designed to be explicit about dependencies and resources to ensure that everything defined in the manifests is both recognized and can be managed appropriately.